The development of a 155 mm Regenerative Liquid Propellant Gun (RLPG) created seal problems between mating cylinders that previously did not exist. The 155 mm RLPG cannon system creates pressures that vary from 0-56000 psi with a total operation pressure impulse of approximately 25 msec. This pressure impulse oscillates at frequencies between 5-55 kHz. The combustion of the liquid propellant used in this RLPG system produces a high temperature, high pressure gaseous nitric acid. In order to overcome these extreme environmental conditions the RLPG seal has to be capable of responding to very quick pressure rise times as well as being environmentally inert. The new seal also had to be capable of withstanding the vibratory action associated with the high frequency pressure impulse fluctuations contained within the cylinders during their operation.
The problem of sealing the interface between two mating cylinders was observed in the early test firing of the RLPG system. In the initial testing a M551 152 mm Sheridan gun seal was used. After approximately 60 firings at low pressures (0-30000 psi), the prior art seal was found to be missing after a general inspection of the gun. Sealing a joint that is not readily accessible or serviceable has been a problem throughout the history of large caliber weapon system design. The RLPG design necessitates the use of an unaccessible joint between a 52 caliber 155 mm gun tube weighing approximately 8000 lbs and a large chamber/combustor cylinder weighing approximately 7000 lbs. The prior art Sheridan gun seal used a thin flexible metal ring which under pressure created a metal-to-metal contact seal. This seal failed because the mechanics of the tube to chamber interaction along with the acidic high temperature high pressure environment was beyond the seals design limitations. These prior art seals were designed for a limited number of low pressure firings where the seal was readily accessible for replacement.